You're on the right track; making guild casltes more accessible is an important part of improving guild life.
Another idea is to allow the guild to purchase a Snoop. Once the snoop has been purchased, guidies can transport to that snoop from any other snoop, an then transport back to that snoop when they're one. An even better (tho less likely) idea would be to allow the guild snoop to send you to any snoop you've opened, but that could potentially cut into transport rune sales, an we can't have that...